Expanding the view controller's interface

All of the new source code will go in ViewController.m. Open the file. After the import statements, let's define the following enumeration to identify the available blending modes:

enum BlendMode {
  None,
  Average,
  Multiply,
  Screen,
  HUD
};

Now, we need to add several new variables and methods to the private interface of our ViewController class. To provide callbacks to a standard image picker, our view controller must implement two protocols, UIImagePickerControllerDelegate and UINavigationControllerDelegate. We also need two more cv::Mat variables to store the selected foreground image in its original format and a converted format that is appropriate for the current background and blending mode. The blending mode is a variable, too. Note the highlighted changes in this block of code:

@interface ViewController () <CvVideoCameraDelegate,
    UIImagePickerControllerDelegate,
    UINavigationControllerDelegate> {
  cv::Mat originalStillMat...